In multi-step manual transmissions for vehicles, which are shifted with interruption of the traction force, i.e., in which an input shaft of the transmission is disengaged from a drive engine by a clutch during the shifting process, the respective gear can be engaged by a form-enclosing shift coupling in that the shift gear teeth of a sliding sleeve are pushed into the coupling gear teeth of a coupling body attached to a gear element to be engaged, for example, to a gear wheel or a transmission housing. When this is done, the torque, in the engaged condition, is transmitted from a gear element via the coupling body, the coupling gear teeth, the shift gear teeth, the sliding sleeve and the sleeve guide, to another gear element, for example, a gear wheel or a shaft, or supported on the transmission housing.
The gear engaged determines the transmission ratio and hence also the speed ratio between the input shaft and the output shaft of the transmission. The uncoupled gear elements, for example, free-running gear wheels of the other gears in mutual engagement, run with a speed difference relative to the engaged gear elements which corresponds to their transmission ratio. When changing from one gear to another, during the shift the components to be coupled must be brought to approximately the same speed before the gear teeth of the sliding sleeve can engage in the coupling gear teeth of the coupling body to be engaged. For this, synchromeshes are used.
The gears are formed of gear wheel assemblies arranged one behind the other, between which there are shift couplings. These are actuated by a shifting device alternately as appropriate for the preselected gear. During this, care must be taken that two shift couplings are not actuated at the same time, because that could damage the transmission, while at the least unpleasant noise is generated and the traction force is interrupted for an undesirably long time. In emergency situations this can have dangerous consequences.
From DE 198 43 584 A1, a shifting device of the type mentioned is known, the full content of which is included herein. To ensure that in every case only one shift coupling is actuated while the other shift couplings remain locked in their neutral position during the shift, a locking shaft arranged parallel to the gearshift shaft is provided, which can be rotated with the gearshift shaft but is arranged axially fixed in the housing. For the locking shaft, a separate suspension must be provided in the gearbox, and room for movement as well as structural space for the locking shaft must also be provided.
The purpose of the present invention is to provide a shifting device for a multi-step transmission, which ensures secure locking of disengaged shift couplings while taking up little structural space.